Extreme Weather
description
Transcript of Extreme Weather
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Thunderstorms, Tornadoes, and Hurricanes
October 27/28 2010
Extreme Weather
Hurricane Ivanover Gulf, Sept. 2004
Source: NOAA
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Definitions
*Climate Change: * Changes in climate of the past, present or future
associated with natural or anthropogenic (human) factors
*Global Warming:* Warming of the 20th and 21st century associated with
anthropogenic activities.
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Weather VS Climate *Weather describes whatever is
happening outdoors in a given place at a given time.
*Weather is what happens from minute to minute.
*can change a lot within a very short time
*Weather includes daily changes in precipitation, barometric pressure, temperature, and wind conditions in a given location.
*Climate describes the total of all weather occurring over a period of years in a given place.
*Climate tells us what it's usually like in the place where you live
Climate is what you expect, weather is what you get!
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Thunderstorms*Begin in cumulus stage*Warm, moist air rises, cools.*Water condenses out of air, releasing heat*Updrafts develop*Precipitation occurs when weight of
precipitation overcomes updrafts
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Thunderstorms*Cloud draws in drier air which
evaporates some moisture, causes cooling. *This cool, dense air sinks,
creating downdrafts*Downdrafts mark mature
thunderstorms*Downdrafts and updrafts make
the thunderstorm cell*Storm may extend to top of
tropopause (~12 km)*#1: Why doesn’t precipitation fall
right as condensation occurs?
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Thunderstorms*A rush of cold air (downdraft) usually occurs
at onset of precipitation*Storms usually dissipate within 15-30 min.*Updrafts weaken, downdrafts dominate*Provide summer rainfall for much of the US*Cooling of up to 10˚C/18˚F on hot summer
days*Strong downdrafts can force more warm air
up, causing multi-cell storms.
Thunderstorm development time lapse (Florida)*http://vimeo.com/4806845
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Severe Thunderstorms
*Stronger winds aloft than at surface vertical wind shear*Tips over top of storm, allows for prolonged
updrafts, longer storm life*Hail forms due to strong updrafts, falls when
heavy enough to overcome updrafts*Strong downdrafts called “microbursts” may
occur, winds up to 146 kt*Dangerous to aviation!
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Source: Wikipedia
Microburst#2: How do you think it could be dangerous to aviation?
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Distribution of Thunderstorms
# days per year thunderstorms observed. Do you think hail follows the same distribution?
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Distribution of Hail #3: How are max/min different here? Why do you think more hail over Rockies, Great Plains?
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Lightning*Lightning occurs to reduce a buildup of positive
and negative charges within a cloud. *+ charged ice crystals tend to be at top of
cloud, and - charged hailstones at bottom. *Area of positive charge on ground develops
below storm*When electrical potential gradient large
enough, the electrical current flows to surface as lightning!*Can have cloud-to-cloud, cloud-to-ground, or
lightning within a cloud.
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http://apollo.lsc.vsc.edu/classes/met130/notes/chapter14/graphics/lightning.mpg
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Lightning*Can heat the air rapidly to 30,000˚C/54,000˚F*This rapid heating causes air to expand and
makes a booming sound wave– thunder!*Sound takes 3 sec to go 1 km, (5 sec per mile)*#4: If you see lightning and hear thunder 15 sec
later, how far away is the lightning?*5 km/3 miles away!*Sometimes thunder is not heard due to the
atmosphere bending the sound waves upward
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Lightning*100 people per year die of lightning
strikes*If about to strike, hair stands on end, skin
tingles, hear clicking sounds
Sept 2003, Carquinez Straits, CAAfter rare influx of moisture from SW
Cloud-to-ground lightning over Las Vegas during SW monsoon season
Source: www.goldengatephotos.com
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Tornadoes*Rapidly rotating winds around intense low
pressure center*Start as funnel-shaped cloud*Diameter of 100-600 meters (300-2000 ft)*Move at 20-40 kt (23-46 mph)*Last only a few minutes*Travel up to 7 km (4 mi)
Source: http://www.cs.uwaterloo.ca
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Tornadoes*Most violent event: April 3 and 4, 1974*148 tornadoes over a 16 hour period*Covered 13 states*307 people killed, 6000 injured*$600 million in damage
Trailer park destroyed in Huntsville, ALF4 tornado over Parker City, IN
Source: http://www.april31974.com
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Tornadoes*Tri-state tornado event March 18, 1925*7 tornadoes across MO, IL, IN*695 people killed!*US has most tornadoes of all countries*Occur in all states, greatest number in
“Tornado Alley”*This is area where cool, dry air from Canada
meets warm, moist air from Gulf
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Source: http://wximpact40-88.pbworks.com
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Tornadoes*Tornado alley susceptible since warm, humid air
overlain by cool air aloft*If strong vertical wind shear occurs and
thunderstorms form, tornadoes likely*Usually occur March-July in late afternoon*Can pick up people, animals, appliances, railroad
cars*220 kt winds max, most < 125 kt*Can pop roofs off/collapse houses! (Bernoulli’s
principle)*#5: How can tornadoes “pop” a roof off a
structure?Tornadoes around the UShttp://www.youtube.com/watch?v=43VoMesUd2Q
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Fujita Scale
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Hurricanes*An intense storm, winds over 64 kt/74 mph*Generally form in tropics (23 1/2˚N/S of
equator)*Warm, humid areas*A “tropical” aka “Easterly” wave in
atmosphere disrupts usual wind flow*In western N Pacific (Asia/Japan), typhoon*In Indian Ocean/Australia, cyclone*Today we will use “hurricane” to refer to all
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Hurricane and SST Change
(Webster et al, 2005, Science)
Webster et al. report that the number of category 4 and 5 hurricanes has almost doubled globally over the past three decades
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Be careful
*Hurricanes are natural events, and are not linearly related to climate change
*Climate change, by increase SST, indeed makes it more possible to have strong hurricane occur
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Anatomy of a hurricane
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Hurricanes*Convergence at surface brings warm, moist air
up*Divergence aloft and sinking air outside the
hurricane, clear skies immediately surrounding
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Hurricanes*Ingredients for Hurricane:*Winds light*Deep layer of high humidity, warm air*Water >80˚F
*Season lasts June-November*Need converging winds, so form in ITCZ*Take in heat at ocean surface, convert it to
kinetic energy as wind*Form between 5˚and 10˚N and S*#6: Why don’t they form over equator?*No Coriolis effect at equator to start “spin”!
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Hurricanes
#7: Why do hurricanes move from East to West?
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Hurricanes*Begins as tropical disturbance/wave*Tropical depression: winds 20-34 kts, closed
isobars*Tropical storm: winds 35-60 kts*Hurricane: winds >64 kts
Hurricane Katrina Source: NOAA
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Atlantic and Pacific Storm tracks, 2010
Source: Washington Post
Source: Wikipedia
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Hurricanes: Why so destructive?*High winds, can collapse structures
*Storm surge!*High wind-driven waves*Low pressure in storm center causes sea
level to rise up to 0.5 m (1.5 ft)! *Like water up a straw
*Strong downbursts*Heavy, sudden rains can cause flooding
Katrina damage in Mississippi
Source: www.katrinadestruction.com
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Hurricane Andrew*August 21, 1992*Hit Louisiana with 120 kt winds*200,000 homes destroyed*$30 billion in damage*53 deaths*Most deaths in US from hurricane:*1900 Galveston, TX: more than 6,000 died!*Confused when calm eye hit, went out to
“check things out”, other side of storm hit suddenly!
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Source: NOAA
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Hurricanes and El Niño*#8: What is El Nino? What are signs it is
happening?*Trade winds over Pacific slacken and/or
reverse, warm water “sloshes” eastward towards coast of Peru. *Causes global climate shifts!*Atlantic: Fewer hurricanes because stronger
upper level winds do not allow formation*Pacific: More hurricanes possible because
more warm water over a larger area
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Naming Hurricanes
Gets name when becomes TSIf major event (like Katrina) name retired for several years
Source: Farmer’s Almanac
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Heat Waves*Definition: A period of several days with
temperatures 5’C (9’F) above average for a given location at a given time of year*Definition varies by region.*Cause 175 deaths a year in US! *During 1980 heat wave, 1250 people died!*Many more die due to secondary effects of heat*Most summers have heat waves*Heat Index- issued by NWS*Gives the “apparent temperature” combining
effects of temperature, humidity, and wind*Ex, “feels like” 104’, actual temp may be 98
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Heat Effects on Body*Sweating dehydrates, causes dizziness and
fainting*In heat, heart pumps more blood*Blood vessels dilate*Body tries to cool blood by getting it closer to
surface- can’t cool if ambient temp too high!*In high humidity, sweat does not evaporate *No cooling of skin
*Also sunburn, stroke, heat exhaustionSource: NOAA/wikipedia
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2010 Russian Heat Wave*Temperatures up to 104’F/40’C for several weeks
*Wildfires, cause poor air quality*Heat like this not seen in 1000 year Russian
climate archives*30% crop decrease expected, ban on crop
exports until 12/31/2010*2000 people drowned trying to escape heat by
bathing in rivers or lakes *Most of them were drunk…
Source: The Economist, Rianovosti
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Global Warming to blame?*Specific weather events cannot be linked to
global warming*Warming and changing of Earth’s surfaces can
increase probability of extreme events*Many extreme events are attributed to normal
oscillations*Ex: Pakistan floods generally associated with La
Nina (ENSO) summer
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Global Warming to blame?*More areas with high Urban Heat Index
*More heat waves*Warm temperatures cause more evaporation*More intense rainfall (in some areas)
*More evaporation*More drought/water shortages (in some areas)
*Warmer oceans*Provide more kinetic energy for stronger hurricanes
*Higher and denser population*Increased chance of fatalities and damage caused by
events*Especially in poorer regions without good
infrastructure